1. Technical Field
Example embodiments of the present invention relate in general to the field of production of 1,1,1,2,3-pentafluoropropane, and, more specifically, to a method and apparatus for continuously producing 1,1,1,2,3-pentafluoropropane with high yield.
2. Related Art
1,1,1,2,3-pentafluoropropane (CF3CHFCH2F, HFC-245eb) is an intermediate useful in manufacture of 2,3,3,3-tetrafluoropropene (CF3CF═CH2, HFO-1234yf), which is effectively used as an alternative refrigerant of chlorofluorocarbon refrigerants, as represented by the following Scheme 1.

A method which includes sequentially performing hydrogenation, dehydrofluorination and hydrogenation of hexafluoropropene (HFP, CF3CF═CF2), as represented by the following Scheme 2, is known in the art as the method of producing HFC-245eb.

However, the method of producing HFO-1234yf as represented by Schemes 1 and 2 has problems in that a raw material, HFP, is relatively expensive, and is a complicated process which is composed of four operations including two hydrogenations and two dehydrofluorinations, which leads to relatively low industrial competitiveness.
A method of producing HFO-1234yf without producing HFC-245eb as an intermediate is a process using 1,1,1,3-tetrachloropropane (CCl3CH2CH2Cl, HCC-250fb) as a raw material. HCC-250fb is produced through a reaction between carbon tetrachloride (CCl4) and ethylene (CH2═CH2) as represented by the following Scheme 3. Here, the carbon tetrachloride and the ethylene are relatively inexpensive and can be readily supplied on a commercial scale.

To produce HFO-1234yf using the HCC-250fb as a starting material, it is necessary to substitute one hydrogen atom bound to a central carbon atom with a halogen atom (F, Cl, Br, or I). In this regard, two methods are known in the related art.
(1) A method of substituting a hydrogen atom bound to carbon in the center of the molecule with a halogen atom before fluorination:
In this method, first, dehydrochlorination, chlorination and dehydrochlorination of HCC-250fb are sequentially carried out to produce 1,1,2,3-tetrachloropropene (CCl2═CClCH2Cl, HCO-1230xa) in which a hydrogen atom of the carbon in the center of the molecule is substituted with a chlorine atom.
Next, the HCO-1230xa is subjected to two operations of hydrofluorination and dehydrochlorination to produce HFO-1234yf.
However, a photo-reaction is included in chlorination during production of the HCO-1230xa, and two by-products, HCO-1230xf (CCl3CCl═CH2) and HCO-1230zd (CCl3CH═CHCl), are also produced in addition to the HCO-1230xa as products of final dehydrochlorination. Therefore, an additional process for converting the by-products into HCO-1230xa is required (see US Publication No. 2012/0022303). Accordingly, the HCO-1230xa is relatively expensive and is not readily distributed on a commercial scale since it is produced with complicated operations as described above.
(2) A method of substituting a hydrogen atom bound to carbon in the center of the molecule with a halogen atom after fluorination:
In this method, first, fluorination and dehydrochlorination of HCC-250fb are carried out to produce 3,3,3-trifluoropropene (CF3CH═CH2, HFO-1243zf), as represented by the following Scheme 4.

Next, the produced HFO-1243zf i) is subjected to chlorination, followed by hydrofluorination to produce HFO-1234yf, as represented by the following Scheme 5, or ii) is simultaneously subjected to chlorination/hydrofluorination (chlorofluorination) to produce HFO-1234yf, as represented by the following Scheme 6.


However, when the reaction is carried out as represented by Scheme 5 or 6, significant amounts of side reaction products such as 1233zd and 1234ze are produced. Therefore, a separate process for handling the 1233zd or 1234ze is required.
In summary, when HFO-1234yf is produced as a next-generation alternative refrigerant, a method of producing 1,1,1,2,3-pentafluoropropane (CF3CHFCH2F, HFC-245eb) as an intermediate has an advantage in that it can be used to produce HFO-1234yf simply and effectively, compared to the other methods. However, when HFP is used as a starting material to produce the HFC-245eb, this is not commercially viable due to its economic inefficiency. On the other hand, when a relatively inexpensive raw material, HCC-250fb, is used without undergoing a process for producing HFC-245eb, a multi-stage process is required. Also, since large amounts of by-products are produced by side reactions, a complicated process for handling the by-products is also required.
Meanwhile, there is a direct fluorination method of directly producing HFC-245eb through a direct reaction of HFO-1243zf with fluorine gas. In this case, however, carbon-carbon cleavage may take place due to high reactivity of the fluorine gas, and many by-products such as HFC-236ea (CF3CHFCHF2), HFC-236cb (CF3CF2CH2F), HFC-227ea (CF3CHFCF3), HFC-227ca (CF3CF2CHF2) and FC-218 (CF3CF2CF3) may be produced. To carry out a fluorination reaction under milder conditions, a method of diluting fluorine gas with an excessive amount of nitrogen gas is known in the art. In this case, however, there are problems related to a localized fluorination reaction and a separation of low-boiling-point products and nitrogen. In particular, it is difficult to take a commercial approach to this method due to difficulty in handling non-reacted fluorine gases.